The present invention relates to an airborne arrangement for the combined display of a topographical moving map and navigational data.
Our invention is applicable to aerial-navigation systems, in which a moving-map display shows the pilot of an aircraft a topographical map which generally corresponds to the region being flown over. In this case, the positioning of the map in the cartesian X and Y directions and the rotational or angular orientation .theta. is controlled automatically as a respective function of the longitude, latitude and heading of the aircraft. The appropriate data (latitude, longitude, heading, etc.) are supplied by the navigational system of the aircraft. The moving-map display includes a computer which carries out servo-control operations in the X, Y and .theta. directions on the basis of the navigational data.
In addition to displaying a topographical or other kind of map, the system also produces an optically projected marker which generally indicates the present position of the aircraft, or else the aircraft's intended destination, or any other desired point on the map.
It is often useful to display other information for navigational purposes, such as speed, fuel consumption, or the course to be followed. This information is generally displayed by a cathode-ray trace employing random scanning in order to form the symbols or alphanumeric characters to be visualized.
According to a known technique, the image of the navigational data displayed on the screen of a cathode-ray tube is mixed optically with that of the movable map, the latter being produced by optical projection and the mixing being performed by means of a semi-reflective mirror. The assembly is arranged to project the two images at infinity and to perform the function of an optical collimator whereby the pilot can look through an optical pupil without the need for accommodation. In another known system, the images are displayed on the screen of a cathode-ray tube, the navigational data and the movable map being projected optically through the rear of the tube. Systems of this nature necessitate the use of a very special tube known as an optical-window tube.
In both of the above arrangements, the opto-mechanical assembly concerned with the projection of the movable map must be situated at only a short distance from the plane of display. Such equipment is heavy, bulky and expensive and takes up a considerable amount of space on the instrument panel, inasmuch as it is usually situated in a low-down viewing position.